1. Field of the Invention
This invention relates to a process for forming modified polyamides. More particularly, this invention relates to a process for forming modified polyamides having advanced melting points as compared to polyamides prepared by other processes. Polyamides treated in accordance with the process of this invention are capable of being fabricated into useful shaped articles of manufacture. e.g., filaments, films, tapes, ribbons. rods, laminates and the like.
2. Description of the Prior Art
Polyamide compositions are disclosed in the prior art as having many and varied uses in industrial and commercial applications. For examples, these polymers can be formed in filament in which the polymer chains are oriented along the filament axis. Such filaments have many uses, in commercial applications, as for example, in the production of fibers for tire cords. textiles and the like. Similarly, these polymer can be fabricated into other useful shaped articles, as for example, gears, lawn mower housings, skate boards and the like.
The melt index of polyamide compositions provides an indication or the viscosity of the polyamides, and their molecular weights. In general, polymers having low melt indexes are desirable because of improved properties of fibers and other shaped articles made therefrom. For example, fibers made from polymers of relatively low melt indexes have increased tensile strength, durability and impact resistance. These properties are very desirable, especially in fibers used as reinforcement for pneumatic automobile tires.
Several processes have been proposed in the prior art for increasing the viscosity and molecular weight of polyamides, as for example, poly(hexamethylene-adipamide). One such method is set forth in U.S. Pat. No. 3,763,113 which discloses a method for increasing the molecular weight of polymers having recurring-CONH-aklylene-NHCO-alkylene units, such as poly(hexamethyleneadidamide) by heating the polyamide with a phosphoric acid derivative in the presence of an inert gas, such as nitrogen. Similarly, U.S. Pat. Nos. 3,551,548 and 3,763,113, each broadly describes a method for increasing the relative viscosity of polyamides, generally, and poly(hexylmethylene adipamide). specifically, by sweeping a molten mixture of the polyamide and phosphorous compound with an inert gas.
Each of these processes provides various adversed effects. For example, in each of the processes, an inert gas is employed, which in high concentrations cause uneven finishing, i.e., a variation in the degree of polymerization, throughout the polyamide, which results in a non-uniform polymer. Furthermore, inert gas is expensive, and requires additional equipment and monitoring which can increase the cost of commercialization of the process, even though the inert gas is used in small amounts.
U.S. Pat. No. 3,509,107 (Brignac. 1970) discloses a process for increasing the relative viscosity of polyamide fibers or copolymides by incorporating a phosphorous or phosphite compound into the polyamide under an inert gas atmosphere. The primary object to Brignac is to provide a process for increasing the viscosity of polyamide yarn and cord which requires a minimum amount of inert gas. U.S. Pat. No. 3,551,548 (Brignac. et al) describes various optimizing procedures for U.S. Pat. No. 3,509,107. The described patents are each directed only to a method of producing polyamide yarn with increased viscosity via incorporating a phosphorous or phosphite compound into the yarn, and then heating said yarn in the presence of inert gas.
British Patent No. 569.184 discloses a method for producing a random copolymer from nylon 6 and nylon 6,6. The invention described therein teaches that heating a mixture of nylon 6 and nylon 6.6 results in interchange between various sections of tube respective polymer molecules with the final product being random copolymer of nylon 6 and nylon 6.6. British Patent No. 569,184 teaches that it is necessary to heat the mixture of homopolymers for periods of time up to 8 hr. at 285.degree. C. without any catalyst.
U.S. Pat. No. 4,390,667 discloses a process for decreasing the melt index and increasing the viscosity of polyamide fibers via incorporating a phosphate compound into the polyamide and heating the polyamide until the desired changes in the melt index and viscosity occur. The phosphates utilized in U.S. Pat. No. 4,390,667 include substituted aryl phosphates which satisfy certain Hammett sigma values.
U.S. Pat. No. 4,417,031 discloses a process for preparing block and graft copolymers. The described process involved reacting two or more polyamides, polyesters, and homopolymers of
.beta.-unsaturated carboxylic acids in order to form a graft and/or block copolymer. Included in the application are copolymers formed from poly(caproamide1 and poly(hexamethylene adinamide).
Diphenyl phosphoryl azide has been used as a convenient reagent for racemization-free peptide synthesis and for polymerization of peptides such as .beta.-alanine and L-alanylglycine. See for example, Nishi, Noro et al. "Polymerization of Amino-acids or Peptides with Diphenyl Phosphoryl Azide (DPPA)". Int. J. Biol. Macromol., Vol. 2, p. 53 (1980) and Shiori, Takavuki. "Diphenylohosphoryl Azide. A New Convenient Reagent for a Modified Curtius Reaction and for the Peptide Synthesis". J. of the American Chemical Society, Vol. 94. p. 6203-6205 (1972).